The reinforcement that reinforcing tires and, notably, motorcycle tires, is currently—and usually—made up of a stack of one or more plies conventionally known as “carcass plies”, “crown plies”, etc. This way of naming the reinforcements stems from the method of manufacture which involves producing a series of semi-finished products in the form of plies, provided with elementary reinforcements, which are often longitudinal, which are subsequently assembled or stacked to build up a green tire. The plies are produced flat, with large dimensions, and are subsequently cut to suit the dimensions of a given product. The plies are also initially assembled in a substantially flat shape. The green tire thus built is then shaped to adopt the toroidal profile typical of tires. The so-called “finishing” semi-finished products are then applied to the green tire to obtain a product ready to be vulcanised.
Such a “conventional” type of method involves, particularly for the phase of building the green tire, the use of an anchoring element (generally a bead wire) which is used to anchor or hold the carcass reinforcement in the region of the heads of the tire. Thus, for this type of method, a portion of all the plies that make up the carcass reinforcement (or just part thereof) is wrapped around a bead wire positioned in the bead of the tire. This then anchors the carcass reinforcement in the bead.
The widespread use throughout industry of this conventional type of method, despite the numerous alternative variations used regarding the creation of the plies and assemblies, has led a person skilled in the art to employ terminology based on the method: hence the generally accepted terminology comprising notably the terms “plies”, “carcass”, “bead wire”, “shaping” to denote the switch from a flat profile to a toroidal profile, etc.
Nowadays there are tires which do not strictly speaking have “plies” or “bead wires” as defined in the above definitions. For example, document EP 0 582 196 describes tires which are manufactured without the use of semi-finished products in the form of plies. For example, the reinforcing elements in the various reinforcing structures are applied directly to the adjacent layers of rubber compound, everything being applied in successive layers to a toroidal form the shape of which makes it possible to obtain directly a profile that can be likened to the final profile of the tire that is being built. Thus, in this case, there are no longer any “semi-finished products”, or any “plies”, or any “bead wires”. The basic products, such as the rubber compounds and the reinforcing elements in the form of threads or filaments, are applied directly to the form. Because this form is of toroidal shape, the green tire no longer has to be shaped in order to change from a flat profile to a profile in the shape of a torus.
Furthermore, the tires described in that document do not have the “traditional” turning back of the carcass ply around a bead wire. That type of anchorage is replaced by an arrangement in which circumferential threads are positioned adjacent to the sidewall reinforcing structure, everything being embedded in a rubber anchoring or cushioning compound.
There are also methods of assembly on a toroidal form that use semi-finished products which are specially designed for rapid, effective and simple laying on a central form. Finally, it is also possible to use a hybrid comprising both certain semi-finished products for creating certain architectural aspects (such as plies, bead wires, etc.), while others are achieved by the direct application of compounds and/or reinforcing elements.
In this document, in order to take account of recent technological advances both in the field of manufacture and in that of the product design, the conventional terms such as “plies”, “bead wires”, etc., are advantageously replaced by neutral terms or terms that are independent of the type of method used. Thus, the term “carcass-type reinforcement” or “sidewall reinforcement” is valid for denoting the reinforcing elements in a carcass ply in the conventional method and the corresponding reinforcing, elements generally applied to the sidewalls of a tire produced using a method that does not employ semi-finished products. The term “anchoring region”, for its part, can just as easily denote the “traditional” wrapping of the carcass ply around a bead wire in a conventional method as it can the assembly formed by the circumferential reinforcing, elements, the rubber compound and the adjacent sidewall reinforcement portions of a bottom region produced using a method involving applying products to a toroidal form.
The longitudinal direction of the tire, or circumferential direction, is the direction corresponding to the periphery of the tire and defined by the direction in which the tire runs. A circumferential plane or circumferential plane of section is a plane perpendicular to the axis of rotation of the tire. The equatorial plane is the circumferential plane that passes through the centre or crown of the tread strip.
The transverse or axial direction of the tire is parallel to the axis of rotation of the tire. The radial direction is a direction that intersects the axis of rotation of the tire and is perpendicular thereto. The axis of rotation of the tire is the axis about which it rotates in normal use. A radial or meridian plane contains the axis of rotation of the tire.
As with all other tires, tires for motorbikes are switching over to a radial design, the architecture of such tires comprising a carcass reinforcement formed of one or two layers of reinforcing elements that make an angle possibly comprised between 65° and 90° with the circumferential direction, the carcass reinforcement being radially surmounted by a crown reinforcement formed of reinforcing elements. There do, however, still remain some non-radial tires to which the invention also relates. The invention also relates to partially radial tires, that is to say tires in which the reinforcing elements of the carcass reinforcement are radial over at least part of the carcass reinforcement, for example in the part corresponding to the crown of the tire. In a variant of the FIG. 3 embodiment wherein at least one of the parts has a varying pitch, the pitch values are such that each pitch value in each of the two intermediate parts 311a and 311b is less than each pitch value in each of the two lateral parts 313a and 313b, each pitch value in each of the two intermediate parts 311a and 311b is less than each pitch value in the central part 312, each pitch value in each of the two lateral parts 313a and 313b is less than each pitch value in the central part 312, the ratio of each value of the pitch in the two lateral parts 313a and 313b to each value of the pitch in the central part 312 is between 0.5 and 0.95, and the ratio of each value of the pitch in the two intermediate parts 311a and 311b to each value of the pitch in the central part 312 is between 0.4 and 0.7.
Numerous crown reinforcement architectures have been proposed, depending on whether the tire is intended to be fitted at the front of the motorbike or at the rear. A first structure, for the crown reinforcement, consists in using only circumferential cords, and the structure is more particularly used for a rear tire. A second structure, taking its inspiration directly from the structures commonly employed in passenger vehicle tires, has been used to improve wear resistance and consists in using at least two working crown layers of reinforcing elements that are substantially mutually parallel within each layer but crossed from one layer to the next making acute angles with the circumferential direction, such tires being more particularly suited to the front of motorbikes. The two working crown layers can be associated with at least one layer of circumferential elements, which are generally obtained by the helical winding of a strip of at least one rubber-coated reinforcing element.
The choice of crown architecture for the tires has a direct impact on certain tire properties such as wear, endurance, grip or even driving comfort or, particularly in the case of motorcycles, stability. However, other tire parameters such as the nature of the rubber compounds used in the tread strip also have an impact on the properties of the tire. The choice and nature of the rubber compounds used in the tread strip are, for example, essential parameters regarding wear properties. The choice and nature of the rubber compounds used in the tread strip also have an impact on the grip of the tire.